I want to perform a nonlinear time history analysis of a steel frame. I am using 3% rayleigh damping for my model. For nonlinear time history analysis, I want to scale the time histories. What should be the value for damping to develop the response spectrum for scaling my time histories.
Generally, 5% is used but as I am using 3% damping in my model. Should I prepare a response spectrum for 3% damping and then do the scaling or should I use the 5% damped response spectrum?
Please help me with this problem.
Thanks.
To generate reduced response spectrum curve you have to calculate effective damping ratio by adding hysteresis damping ratio in 5% damping ratio.
i.e, effective damping = 5% + Ed/(4π×Eso)
Where 5% is material damoing and rest is hysteresis damping.
Where Ed and Eso can be calculated using hysteresis loop in bilinear idealization.
By another method recommended in ATC-40 is use of reduction factor.
R.F=sqrt(10/5+damping ratio)
And multiply ordinates of 5% demand curve by R.F to obtain reduced demand curve.
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